1. Field of the Disclosure
The present disclosure relates to an organic electroluminescent device (hereinafter, referred to as an “OLED”), and more particularly, to a flexible organic electroluminescent device for blocking moisture from being infiltrated into the organic electroluminescent device to enhance the life of the organic electroluminescent device, and a method for fabricating the same.
2. Description of the Related Art
An organic electroluminescent device, which is one of types of flat panel displays (FPDs), has high brightness and low operation voltage characteristics. Furthermore, the organic electroluminescent device has a high contrast ratio because of being operated as a self-luminous type display that spontaneously emits light, and allows the implementation of an ultra-thin display. The organic light-emitting diode also has advantages such as facilitating the implementation of moving images using a response time of several microseconds (μs), having no limitation in viewing angle, having stability even at low temperatures, and being driven at low voltages between DC 5 to 15 V, thus facilitating the fabrication and design of a driving circuit thereof.
Furthermore, the fabrication process of the organic electroluminescent device can be carried out using only deposition and encapsulation equipment, and therefore the fabrication process is very simple.
The organic light-emitting diode having such characteristics can be largely divided into a passive matrix type and an active matrix type, and in the passive matrix type, a device may be configured with a matrix form in which the scan and signal lines are crossed with each other, and the scan lines are sequentially driven as time passes to drive each pixel, and thus instantaneous brightness as much as average brightness multiplied by the number of lines may be required to display the average brightness.
However, the active matrix type has a structure in which thin-film transistors, which are switching devices for turning on or off a pixel region, are located for each pixel region, and drive transistors connected to the switching transistors are connected to a power line and organic light emitting diodes, and formed for each pixel region.
Here, a first electrode connected to the drive transistor may be turned on or off in the pixel region unit, and a second electrode facing the first electrode may perform the role of a common electrode, thereby implementing an organic light emitting diode along with an organic light emitting layer interposed between the two electrodes.
In the active matrix type having such characteristics, a voltage applied to the pixel region may be charged at a storage capacitance (Cst), and applied until the next frame signal is applied and thus continuously driven for one screen regardless of the number of scan lines.
Accordingly, the same brightness can be obtained even if a low current is applied, thereby having an advantage of providing low power consumption, fine pitch and large screen sized display, and thus in recent years, active matrix type organic electroluminescent devices have been widely used.
The fundamental structure and operating characteristics of such an active matrix type organic electroluminescent device will be described below with reference to the accompanying drawings.
FIG. 1 is a circuit diagram for one pixel region in a typical active matrix type organic electroluminescent device.
Referring to FIG. 1, one pixel region of a typical active matrix type organic electroluminescent device 10 may include a switching thin film transistor (STr), a drive thin film transistor (DTr), a storage capacitor (Cst), and an organic light emitting diode (E).
A gate line (GL) is formed in the first direction, and a data line (DL) disposed in the second direction crossed with the first direction to define a pixel region (P) along with the gate line (GL) is formed, and a power line (PL) separated from the data line (DL) to apply a power voltage is formed.
A switching thin film transistor (STr) is formed at a portion where the data line (DL) and gate line (GL) are crossed with each other, and a drive thin film transistor (DTr) electrically connected to the switching thin film transistor (STr) is formed within the each pixel region (P).
The drive thin film transistor (DTr) is electrically connected to the organic light emitting diode (E). In other words, a first electrode, which is one side terminal of the organic light emitting diode (E), is connected to a drain electrode of the drive thin film transistor (DTr), and a second electrode, which is the other terminal thereof, is connected to the power line (PL). Here, the power line (PL) transfers a power voltage to the organic light emitting diode (E). Furthermore, a storage capacitor (Cst) is formed between a gate electrode and a source electrode of the drive thin film transistor (DTr).
Accordingly, when a signal is applied through the gate line (GL), the switching thin film transistor (STr) is turned on, and the signal of the data line (DL) is transferred to the gate electrode of the drive thin film transistor (DTr) to turn on the drive thin film transistor (DTr), thereby emitting light through the organic light emitting diode (E). Here, when the drive thin film transistor (DTr) is in a turned-on state, the level of a current flowing through the organic light emitting diode (E) from the power line (PL) is determined, and due to this, the organic light emitting diode (E) may implement a gray scale, and the storage capacitor (Cst) may perform the role of constantly maintaining the gate voltage of the drive thin film transistor (DTr) when the switching thin film transistor (STr) is turned off, thereby allowing the level of a current flowing through the organic light emitting diode (E) to be constantly maintained up to the next frame even when the switching thin film transistor (STr) is in an off state.
FIG. 2 is a plan view schematically illustrating a plurality of sub-pixel regions of an organic electroluminescent device according to the related art, as a schematic view showing moisture being infiltrated through one sub-pixel region and diffused up to adjoining sub-pixel regions.
FIG. 3 is a schematic cross-sectional view of an organic electroluminescent device according to the related art.
FIG. 4 is a schematic enlarged cross-sectional view of an organic electroluminescent device according to the related art, as an enlarged cross-sectional view schematically illustrating moisture infiltrated through a bank being diffused along the bank.
Referring to FIG. 2, in an organic electroluminescent device 10 according to the related art, a display area (AA) is defined on a substrate 11, and a non-display area (NA) is defined at the outside of the display area (AA), and a plurality of pixel regions (P), each defined as a region surrounded by the gate line (not shown) and the data line (not shown) are provided, and the power line (not shown) is provided in parallel to the data line (not shown) in the display area (AA).
A switching thin film transistor (STr) (not shown) and a drive thin film transistor (DTr) (not shown) are formed in the plurality of pixel regions (SP), respectively, and connected to the drive thin film transistor (DTr).
In the organic electroluminescent device 10 according to the related art, the substrate 11 formed with the drive thin film transistor (DTr) and organic light emitting diode (E) is encapsulated by a passivation layer (not shown).
Specifically describing the organic electroluminescent device 10 according to the related art, as illustrated in FIG. 3, the display area (AA) is defined, and the non-display area (NA) is defined at the outside of the display area (AA) on the substrate 11, and a plurality of pixel regions (P), each defined as a region surrounded by the gate line (not shown) and the data line (not shown) are provided, and the power line (not shown) is provided in parallel to the data line (not shown) in the display area (AA).
An insulation material, for example, a buffer layer (not shown) formed of silicon oxide (SiO2) or silicon nitride (NiNx), which is an inorganic insulation material, is provided on the substrate 11.
A semiconductor layer 13 made of pure polysilicon to correspond to the drive region (not shown) and switching region (not shown), respectively, and comprised of a first region 13a forming a channel at the central portion thereof and second regions 13b and 13c in which a high concentration of impurities are doped at both lateral surfaces of the first region 13a is formed at each pixel region (SP) within the display area (AA) at an upper portion of the buffer layer (not shown).
A gate insulating layer 15 is formed on the buffer layer (not shown) including the semiconductor layer 13, and the drive region (not shown) and switching region (not shown) are provided on the gate insulating layer 15, and thus a gate electrode 17 is formed to correspond to the first region 13a of each of the semiconductor layer 13.
A gate line (not shown) connected to a gate electrode (not shown) formed in the switching region (not shown) and extended in one direction is formed on the gate insulating layer 15.
An interlayer insulating layer 19 is formed on an entire surface of the display area on the gate electrode 17 and gate line (not shown). A semiconductor layer contact hole (not shown) for exposing the second regions 13b and 13c, respectively, located at both lateral surfaces of the first region 13a of each of the semiconductor layer, is provided on the interlayer insulating layer 19 and the gate insulating layer 15 at a lower portion thereof.
A data line (not shown) crossed with a gate line (not shown) to define the pixel region (SP) and formed of a second metal material, and a power line (not shown) separated therefrom are formed at an upper portion of the interlayer insulating layer 19 including the semiconductor layer contact hole (not shown). Here, the power line (not shown) may be formed to be separated from and in parallel to the gate line (not shown) on a layer formed with the gate line (not shown), namely, the gate insulating layer.
A source electrode 23a and a drain electrode 23b brought into contact with the second regions 13b and 13c separated from each other, and respectively exposed through the semiconductor layer contact hole (not shown) and formed of the same second metal material as that of the data line (not shown) are formed in the each drive region (not shown) and switching region (not shown) on the interlayer insulating layer 19. Here, the semiconductor layer and gate insulating layer sequentially deposited on the drive region (not shown) and the gate electrode 17 and interlayer insulating layer 19 and the source electrode 23a and drain electrode 23b formed to be separated from each other forms a drive thin film transistor (DTr).
An organic insulating layer 25 having a drain contact hole (not shown) for exposing the drain electrode 23b of the drive thin film transistor (DTr) is formed on the drive thin film transistor (DTr) and switching thin film transistor (not shown).
A first electrode 31 brought into contact with the drain contact hole (not shown) through the drain electrode 23b and the drain contact hole (not shown) of the drive thin film transistor (DTr) and having a separated form for each pixel region (SP) is formed on the organic insulating layer 25.
A bank 33 formed to divide each pixel region (SP) is formed on the first electrode 31. Here, the bank 33 is disposed between adjoining pixel regions (SPs).
An organic light emitting layer 35 comprised of organic light emitting patterns (not shown) for emitting red, green and blue colors, respectively, is formed on the first electrode 31 within each of the pixel region (SP) surrounded by the bank 33.
A second electrode 37 is formed on an entire surface of the display area (AA) at an upper portion of the organic light emitting layer 35 and bank 33. Here, the first electrode 31 and second electrode 37 and the organic light emitting layer 35 interposed between the two electrodes 31 and 37 form an organic light emitting diode (E).
A first passivation layer 39 is formed on an entire surface of the substrate including the second electrode 37.
A high organic molecular substance such as a polymer is coated over the first passivation layer 39 to form an organic layer 41.
A second passivation layer 43 is additionally formed on an entire surface of the substrate including the organic layer 41 to block moisture from being infiltrated through the organic layer 41.
Moreover, though not shown in the drawing, an adhesive is located on an entire surface of the substrate including the second passivation layer 43 to face a barrier film (not shown) for the encapsulation of the organic light emitting diode (E), and the adhesive (not shown) is completely glued to the substrate 11 and barrier film (not shown) and interposed between the substrate 11 and barrier film (not shown).
In this manner, the organic electroluminescent device 10 according to the related art is configured by fixing the substrate 101 to the barrier film (not shown) through the adhesive (not shown) to form a panel state.
As described above, according to an organic electroluminescent device according to the related art, when there exists a defect in the barrier film (not shown) for encapsulation as illustrated in FIGS. 2 and 4, moisture is infiltrated into the pixel region (SP) through the defect and the organic insulating layer 25 which is a planarization layer or infiltrated into the pixel region (SP) through the defect and the bank 33. In particular, when moisture is infiltrated through the bank 33, the moisture is diffused along the bank 33, which is an organic material, thereby causing all the adjoining pixel regions (SPs) to be defective since the bank 33 is adjacent to the adjoining pixel regions (SPs).
According to the related art, when a planarization layer, namely, an organic insulating layer, is not formed in the non-display area to block moisture from being infiltrated into the pixel region (SP) through the defect or planarization layer, it may cause deteriorate the quality due to a step at the inorganic layer or the like disposed on the organic electroluminescent device.
In addition, according to the related art, even when the bank is divided to block moisture from being infiltrated into the pixel region (SP) through the defect or planarization layer, the moisture may be diffused through an organic insulating layer located at a lower portion thereof, and thus there is a limit in preventing moisture from being infiltrated into the pixel region (SP).